A gallium nitride/sapphire thin film, which is useful for an optoelectronic device (eg., LED, LD) or other electronic devices as a substrate, has been conventionally prepared by growing gallium nitride on a sapphire substrate using metal organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxy (HVPE), etc. The gallium nitride/sapphire thin film suffers from bending deformation due to interfacial strain caused by the differences in the lattice parameter and thermal expansion coefficient between sapphire and gallium nitride. The degree of the bending deformation increases as the thickness of a gallium nitride (GaN) layer increases, as can be seen in FIG. 1. Such bending deformation adversely affects the quality and productivity of an optoelectronic and electronic device comprising the gallium nitride/sapphire thin film as a substrate.
In order to reduce such bending deformation, U.S. Pat. No. 6,829,270 discloses a gallium nitride/sapphire thin film obtained by using a sapphire substrate having a thickness of 700 μm much thicker than 430 μm which is commercially available but undergoes increased bending deformation on the growth of gallium nitride thereon.
U.S. Pat. No. 6,528,394 discloses a method for growing gallium nitride having an interface with an embossed shape between a GaN layer and a sapphire substrate by carrying out a first nitridation, a surface-treatment with ammonia (NH3) and hydrogen chloride (HCl) and a second nitridation, in succession, to form an aluminum nitride (AlN) interface, before the growth of gallium nitride.
On studying a gallium nitride/sapphire thin film having a reduced bending deformation and a sufficiently thick gallium nitride layer, the present inventors have found that the bending deformation can be further reduced by controlling the number and size of the embossings formed on an AlN interface between the GaN layer and the sapphire substrate, and this is obtained under various thickness conditions of the sapphire substrate including 430 μm which is commercially available.